Re: old cyanotype formulae

["alnovo@inwind.it" <alnovo@inwind.it>]

Wonderful, Charlie.

I need only a little explanation:

> Photography Theory and Practice by Clerc dated 1930 gives two formulae- one
> for green citrate and one for brown:
> Green:
>        Potassium Ferrocyanide

Is this correct? I have found only one formula using ferrocyanide (saturated, with 50% brown fe. am. citr.), but I believed this was a mistake.

> Photographic Chemistry Vol. One Pierre Glafkides English edition dated 1958
> from the French edition dated 1957
>
> Ferric Ammonium Citrate formulas:
> PH < 2.3            Ferric Ammonium Citrate(green) 25%                  100cc
>                          Potassium Ferricyanide 12%
>    100cc
>
> PH> 2.3             Ferric Ammonium Citrate(brown) 20%                 100cc
>                          Potassium Ferricyanide 16%
>    100cc
>                          Ammonia
>               1-4cc
> He states:"the addition of small quantities of dichromate increases the
> contrast. Triethanolamine (1cc) increases the sensitivity and reduces the
> contrast."


It is interesting to note that in http://jchemed.chem.wisc.edu/Journal/Issues/2001/Mar/abs311_2.html is reported an experimental study on the iron/ferricianyde photochemistry, stating that the maximun quantum jeld is in the 2-5 pH range, and that the NH4 ion is essential for the whole reaction.



Alberto

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